A diagram illustrating how settlement at a bridge approach is repaired. Sampyo said Thursday its "special mortar" can be used to fix elevation gaps caused by ground subsidence at bridge approach sections. [Graphic=ChatGPT]
A diagram illustrating how settlement at a bridge approach is repaired. Sampyo said Thursday its "special mortar" can be used to fix elevation gaps caused by ground subsidence at bridge approach sections. [Graphic=ChatGPT]

Pumped beneath bridge approaches to fill voids — no vibration compaction needed

Balanced fluidity and viscosity prevent material separation; curing takes about two to three days

Seoul finds elevation gaps at 11 Han River bridges; Sampyo Industries pushes to expand repair method

A specialized cement product called Sampyo Special Mortar was used in elevation-gap repair work at Seoul's Seongsu Bridge and Olympic Bridge. When pumped in, the material flows on its own into voids beneath structures without requiring separate vibration compaction, filling gaps caused by ground subsidence and improving the load-bearing condition of the structure. The product is designed to flow freely like water while preventing the separation of cement and sand, combining the fluidity and viscosity needed to fill narrow, complex spaces.

According to Sampyo Industries and construction industry sources, one of the main causes of elevation gaps at bridge approach sections is the difference in the foundational structures supporting the road and the bridge. Although the surface appears to be a single continuous road, the underlying structures differ. Bridges are typically supported by pile foundations anchored deep in solid bedrock, while approach roads are often built on compacted fill layers of soil. Over time, a height difference develops between the two structures.

The most common scenario is the gradual settling of the fill layer beneath an approach road under the repeated load of vehicles or due to rainwater infiltration. While the bridge, resting on a comparatively firm foundation, holds its position, the approach road subsides as soil is displaced — creating the elevation gap. The problem goes beyond a simple difference in surface height. When the soil beneath an approach road sinks, a void can form between the concrete structure supporting the road and the fill layer below it, meaning the road may appear intact on the surface while losing adequate support underneath.

In August, the Seoul Metropolitan Government conducted a full inspection of all 22 Han River bridges in the city using 11 external experts and found elevation gaps at 32 approach ramps across 11 bridges. No direct safety hazards were identified, however. The city said it would prioritize reinforcing the ground at the south B-ramp of Seongsu Bridge and the B-ramp of Olympic Bridge, where the gaps were relatively large, and would continue monitoring changes going forward. The special mortar developed by Sampyo was used in that reinforcement work.

Mortar is generally a construction material made by mixing cement, sand and water. It is widely used to finish wall surfaces or level floors. Filling the narrow gaps beneath a bridge with ordinary mortar, however, is not straightforward. If the mixture is too thick, it cannot flow into tight corners. Adding too much water, on the other hand, can cause cement particles and sand to separate, and can also weaken the strength and durability of the hardened material.

For this reason, high-fluidity mortar must achieve both flowability and material stability at the same time. In the construction materials field, this is accomplished through high-performance water-reducing agents that prevent cement particles from clumping together, along with viscosity-control technology that suppresses material separation. The water-reducing agents help disperse cement particles so the mixture flows well without requiring excessive water.

"Thanks to its high-fluidity properties, the material flows on its own into complex structural interiors and narrow gaps, filling them densely without the need for separate vibration compaction," a Sampyo Industries official said. "Its own weight and excellent self-leveling properties allow it to form a uniform horizontal surface."

Self-leveling refers to the property by which a material's surface becomes flat as it flows. Once the special mortar fills the voids beneath a structure and hardens, it can improve the load-bearing condition of that section. According to Sampyo Industries, the special mortar used in this project took about two to three days to cure.


hong@heraldcorp.com